Five near-infrared-emissive graphene quantum dots for multiplex bioimaging

Area of Science:

• Materials Science
• Biomedical Engineering
• Nanotechnology

Background:

• Near-infrared (NIR) fluorescence imaging offers deep tissue penetration and low background autofluorescence, making it valuable for diagnostics.
• Existing NIR fluorophores often lack therapeutic delivery, possess poor photostability, and raise toxicity concerns.
• Graphene quantum dots (GQDs) are emerging as promising nanomaterials due to their unique optical and electronic properties.

Purpose of the Study:

• To develop and evaluate biocompatible graphene quantum dots (GQDs) with spectrally-separated fluorescence in the near-infrared (NIR) range.
• To investigate the origin of NIR optical properties in GQDs using theoretical calculations.
• To assess the potential of these GQDs for in vitro cellular imaging and multiplexing.

Main Methods:

• Synthesis and characterization of five types of biocompatible GQDs doped with rare-earth metals or nitrogen, or derived from reduced graphene oxide.
• Hartree-Fock calculations to determine the origin of NIR fluorescence.
• In vitro cell internalization studies in HEK-293 cells.
• Optical property measurements including quantum yield and photostability.
• Simultaneous multiplex imaging in NIR-I and NIR-II spectral windows.

Main Results:

• Five types of GQDs exhibited spectrally-separated NIR fluorescence (928-1053 nm) upon NIR excitation.
• NIR optical properties were attributed to rare-earth metal doping or defect states, confirmed by Hartree-Fock calculations.
• GQDs demonstrated moderate quantum yields (up to 1.34%) and excellent photostability (>4 h).
• Biocompatible concentrations of GQDs (0.5-2 mg ml^-1) were successfully internalized into HEK-293 cells for in vitro imaging.
• Simultaneous multiplex imaging in NIR-I and NIR-II was achieved using the developed GQD platforms.

Conclusions:

• The developed biocompatible GQDs possess tunable NIR fluorescence, high photostability, and excellent biocompatibility.
• These novel GQD platforms enable simultaneous multiplex imaging in distinct NIR spectral regions.
• The findings suggest significant potential for these GQDs in multianalyte testing and multiwavelength bioimaging, particularly for combination therapies.